MATURITY AND PETROLEUM SYSTEMS MODELLING IN THE OFFSHORE ZAMBEZI DELTA DEPRESSION AND ANGOCHE BASIN, NORTHERN MOZAMBIQUE
E.S.Mahanjane*1,2,3, D.Franke2, R. Lutz2, J. Winsemann3, A. Ehrhardt2, K. Berglar2 and C. Reichert2
1 Instituto Nacional de Petróleo (INP) – Av. Fernão Magalhaes N. 34 - 2° Andar, PO Box 4724 Maputo, Mozambique.
2 Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stillweg 2, 30655 Hannover, Germany.
3 Institut für Geologie, Leibniz Universität Hannover, Callinstraße 30, 30167 Hannover, Germany.
Petroleum systems analysis and maturity modelling is used to predict the timing and locations of hydrocarbon generation in the underexplored offshore Zambezi Delta depression and Angoche basin, northern Mozambique. Model inputs include available geological, geochemical and geophysical data. Based on recent plate-tectonic reconstructions and regional correlations, the presence of Valanginian and Middle and/or Late Jurassic marine source rock is proposed in the study area.
The stratigraphy of the Mozambique margin was interpreted along reflection seismic lines and tied to four wells in the Zambezi Delta depression. Thermal maturity was calibrated against measured vitrinite reflectance values from these four wells. Four 1-D models with calibration data were constructed, together with another five without calibration data at pseudo-well locations, and indicate the maturity of possible source rocks in the Zambezi Delta depressions and Angoche basin. Two 2-D petroleum systems models, constrained by seismic reflection data, depict the burial history and maturity evolution of the Zambezi Delta basin. With the exception of the deeply-buried centre of the Zambezi Delta depression where potential Jurassic and Lower Cretaceous source rocks were found to be overmature for both oil and gas, modelling showed that potential source rocks in the remaining parts of the study area are mature for hydrocarbon generation.
In both the Zambezi Delta depression and Angoche basin, indications for natural gas may be explained by early maturation of oil-prone source rocks and secondary oil cracking, which likely began in the Early Cretaceous. In distal parts of the Angoche basin, however, the proposed source rocks remain in the oil window.
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